(reflect) Have TypeVariable extend AnnotatedElement

When annotations were added to the platform by JSR 175 in JDK 5, annotations could *not* be applied to the declarations of type parameters of classes, methods, and constructors.

For regularity of the language model and core reflections and to support forthcoming functionality expected in JSR 308, it would be helpful if java.lang.reflect.TypeVariable extended AnnotatedElement even if the implementation was only vacuous.